Prostate Tumor Growth In Mice Research Articles

Manzamine A reduces androgen receptor transcription and synthesis by blocking E2F8-DNA interactions and effectively inhibits prostate tumor growth in mice.

The androgen receptor (AR) is the main driver in the development of castration-resistant prostate cancer, where the emergence of AR splice variants leads to treatment-resistant disease. Through detailed molecular studies of the marine alkaloid manzamine A (MA), we identified transcription factor E2F8 as a previously unknown regulator of AR transcription that prevents AR synthesis in prostate cancer cells. MA significantly inhibited the growth of various prostate cancer cell lines and was highly effective in inhibiting xenograft tumor growth in mice without any pathophysiological perturbations in major organs. MA suppressed the full-length AR (AR-FL), its spliced variant AR-V7, and the AR-regulated prostate-specific antigen (PSA; also known as KLK3) and human kallikrein 2 (hK2; also known as KLK2) genes. RNA sequencing (RNA-seq) analysis and protein modeling studies revealed E2F8 interactions with DNA as a potential novel target of MA, suppressing AR transcription and its synthesis. This novel mechanism of blocking AR biogenesis via E2F8 may provide an opportunity to control therapy-resistant prostate cancer over the currently used AR antagonists designed to target different parts of the AR gene.

Stromal-derived MAOB promotes prostate cancer growth and progression.

Prostate cancer (PC) develops in a microenvironment where the stromal cells modulate adjacent tumor growth and progression. Here, we demonstrated elevated levels of monoamine oxidase B (MAOB), a mitochondrial enzyme that degrades biogenic and dietary monoamines, in human PC stroma, which was associated with poor clinical outcomes of PC patients. Knockdown or overexpression of MAOB in human prostate stromal fibroblasts indicated that MAOB promotes cocultured PC cell proliferation, migration, and invasion and co-inoculated prostate tumor growth in mice. Mechanistically, MAOB induces a reactive stroma with activated marker expression, increased extracellular matrix remodeling, and acquisition of a protumorigenic phenotype through enhanced production of reactive oxygen species. Moreover, MAOB transcriptionally activates CXCL12 through Twist1 synergizing with TGFβ1-dependent Smads in prostate stroma, which stimulates tumor-expressed CXCR4-Src/JNK signaling in a paracrine manner. Pharmacological inhibition of stromal MAOB restricted PC xenograft growth in mice. Collectively, these findings characterize the contribution of MAOB to PC and suggest MAOB as a potential stroma-based therapeutic target.

Targeting prostate tumor low-molecular weight tyrosine phosphatase for oxidation-sensitizing therapy.

Protein tyrosine phosphatases (PTPs) play major roles in cancer and are emerging as therapeutic targets. Recent reports suggest low-molecular weight PTP (LMPTP)-encoded by the ACP1 gene-is overexpressed in prostate tumors. We found ACP1 up-regulated in human prostate tumors and ACP1 expression inversely correlated with overall survival. Using CRISPR-Cas9-generated LMPTP knockout C4-2B and MyC-CaP cells, we identified LMPTP as a critical promoter of prostate cancer (PCa) growth and bone metastasis. Through metabolomics, we found that LMPTP promotes PCa cell glutathione synthesis by dephosphorylating glutathione synthetase on inhibitory Tyr270. PCa cells lacking LMPTP showed reduced glutathione, enhanced activation of eukaryotic initiation factor 2-mediated stress response, and enhanced reactive oxygen species after exposure to taxane drugs. LMPTP inhibition slowed primary and bone metastatic prostate tumor growth in mice. These findings reveal a role for LMPTP as a critical promoter of PCa growth and metastasis and validate LMPTP inhibition as a therapeutic strategy for treating PCa through sensitization to oxidative stress.

MAOA-mediated reprogramming of stromal fibroblasts promotes prostate tumorigenesis and cancer stemness.

The tumor microenvironment plays a critical role in prostate cancer (PC) development and progression. Inappropriate activation of the stroma potentiates the growth and transformation of epithelial tumor cells. Here, we show that upregulation of monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines, in stromal cells elevates production of reactive oxygen species, triggers an inflammatory response including activation of IL-6, and promotes tumorigenesis in vitro and in vivo. Mechanistically, MAOA enhances IL-6 transcription through direct Twist1 binding to a conserved E-box element at the IL-6 promoter. MAOA in stromal fibroblasts provides tumor cell growth advantages through paracrine IL-6/STAT3 signaling. Tissue microarray analysis revealed co-expression correlations between individual pairs of proteins of the stromal MAOA-induced Twist1/IL-6/STAT3 pathway in clinical specimens. Downstream of stromal MAOA, STAT3 also promotes cell stemness and transcriptionally activates expression of cancer stem cell marker CD44 in PC cells. MAOA inhibitor treatment effectively suppressed prostate tumor growth in mice in a stroma-specific targeted manner. Collectively, these findings characterize the contribution of MAOA to stromal activation in PC pathogenesis and provide a rationale for targeting MAOA in stromal cells to treat PC.

A low carbohydrate, high protein diet suppresses intratumoral androgen synthesis and slows castration-resistant prostate tumor growth in mice

Dietary factors continue to preside as dominant influences in prostate cancer prevalence and progression-free survival following primary treatment. We investigated the influence of a low carbohydrate diet, compared to a typical Western diet, on prostate cancer (PCa) tumor growth in vivo. LNCaP xenograft tumor growth was studied in both intact and castrated mice, representing a more advanced castration resistant PCa (CRPC). No differences in LNCaP tumor progression (total tumor volume) with diet was observed for intact mice (P=0.471) however, castrated mice on the Low Carb diet saw a statistically significant reduction in tumor growth rate compared with Western diet fed mice (P=0.017). No correlation with serum PSA was observed. Steroid profiles, alongside serum cholesterol and cholesteryl ester levels, were significantly altered by both diet and castration. Specifically, DHT concentration with the Low Carb diet was 58% that of the CRPC-bearing mice on the Western diet. Enzymes in the steroidogenesis pathway were directly impacted and tumors isolated from intact mice on the Low Carb diet had higher AKR1C3 protein levels and lower HSD17B2 protein levels than intact mice on the Western diet (ARK1C3: P=0.074; HSD17B2: P=0.091, with α=0.1). In contrast, CRPC tumors from mice on Low Carb diets had higher concentrations of both HSD17B2 (P=0.016) and SRD5A1 (P=0.058 with α=0.1) enzymes. There was no correlation between tumor growth in castrated mice for Low Carb diet versus Western diet and (a) serum insulin (b) GH serum levels (c) insulin receptor (IR) or (d) IGF-1R in tumor tissue. Intact mice fed Western diet had higher serum insulin which was associated with significantly higher blood glucose and tumor tissue IR. We conclude that both diet and castration have a significant impact on the endocrinology of mice bearing LNCaP xenograft tumors. The observed effects of diet on cholesterol and steroid regulation impact tumor tissue DHT specifically and are likely to be mechanistic drivers behind the observed tumor growth suppression.

Anibamine, a natural product CCR5 antagonist, as a novel lead for the development of anti-prostate cancer agents

Accumulating evidence indicates that the chemokine receptor CCR5 and the chemokine CCL5 may be involved in the proliferation and metastasis of prostate cancer. Consequently, chemokine receptor CCR5 antagonists could potentially act as anti-prostate cancer agents. As the first natural product CCR5 antagonist, anibamine provides a novel chemical structural skeleton compared with other known antagonists identified through high-throughput screening. Our studies demonstrate that anibamine produces significant inhibition of prostate cancer cell proliferation at micromolar to submicromolar concentrations as well as suppressing adhesion and invasion of the highly metastatic M12 prostate cancer cell line. Preliminary in vivo studies indicate that anibamine also inhibits prostate tumor growth in mice. These findings indicate that anibamine may prove to be a novel lead compound for the development of prostate cancer therapeutic agents.

Effects of Plasmid-Based Stat3-Specific Short Hairpin RNA and GRIM-19 on PC-3M Tumor Cell Growth

Persistent activation of signal transducers and activators of transcription 3 (Stat3) and its overexpression contribute to the progression and metastasis of several different tumor types. For this reason, Stat3 is a reasonable target for RNA interference-mediated growth inhibition. Blockade of Stat3 using specific short hairpin RNAs (shRNA) can significantly reduce prostate tumor growth in mice. However, RNA interference does not fully ablate target gene expression in vivo, owing to the idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of Stat3-specific shRNA, we applied a combination treatment involving gene associated with retinoid-IFN-induced mortality 19 (GRIM-19), another inhibitor of STAT3, along with shRNA. The coding sequences for GRIM-19, a cellular STAT3-specific inhibitor, and Stat3-specific shRNAs were used to create a dual expression plasmid vector and used for prostate cancer therapy in vitro and in mouse xenograft models in vivo. The coexpressed Stat3-specific shRNA and GRIM-19 synergistically and more effectively suppressed prostate tumor growth and metastases when compared with treatment with either single agent alone. The simultaneous use of two specific, but mechanistically different, inhibitors of STAT3 activity exerts enhanced antitumor effects.